ACTION OF RENNIN 



357 



solved in i per cent dilute hydrochloric acid, acid albumin. Test for the pro- 

 teid reactions. 



After two hours filter the remaining 60 c.c., exactly neutralize to remove 

 any traces of acid albumin, and filter. The filtrate contains proteoses. Con- 

 centrate the filtrate over a water bath to one-fourth its volume, add an equal 

 quantity of saturated ammonium-sulphate solution, a sticky precipitate of 

 primary proteoses separates out. Collect on a filter paper, wash with half- 

 saturated ammonium sulphate, redissolve in very dilute salt-solution, and 

 test for proteid reactions. The primary proteoses are precipitated by nitric 

 acid. 



To the filtrate from the half -saturated ammonium sulphate add crystals of 

 ammonium sulphate until complete saturation with salt. Deutero-albumoses 



separate out. Collect on a filter paper, wash, dissolve, and test for proteids. 

 The secondary proteoses are not precipitated by nitric acid. 



Finally the filtrate contains peptone. It can be isolated and tested by 

 concentrating over the water bath, adding barium hydrate to slight excess 

 to remove the sulphate, filtering, and precipitating the excess of barium by 

 exact neutralization with i per cent sulphuric acid. Test for proteid reac- 

 tions. Peptone gives a rose color in the biuret reaction. The xanthoproteic 

 reaction gives the color change, but not the usual precipitate. Peptone is re- 

 dissolved from its alcoholic precipitate without change. It is dialyzable. 



15. Action of Rennin. Add a solution of commercial rennin (jun- 

 ket powder), or of the extract of gastric mucous membrane of the fourth 

 stomach of a calf, to 5 c.c. of milk and let stand for a few minutes. Repeat 

 the test with artificial gastric juice. Also with neutral gastric juice. In each 

 case the milk will form a jelly-like clot, which is firmer in the test tube contain- 

 ing commercial rennin. In the test tube containing artificial gastric juice, 



